[GRASS-user] the performance of displaying vector attributes

[Zbigniew Perski]

On Sun, 2006-11-12 at 12:33 +0100, Moritz Lennert wrote:
> Hello Zbigniew,
> (Cc to Michael and Glynn as they are currently busy reworking
> d.vect.thematic)
> 
I have couple of suggestions:
1. There is an option to remove outline of the symbols. If you are using
small size (say: 3 to 5)basic/circle the map looks ugly. I propose to
change no outline into outline color =  fill color. I have modified in
such way d.vect.thematic and the output looks much better now.

2. Allow full color scale apart from the scaling between two colors. I
created a script which is doing that. It is very slow and I started to
test different approach now: to further modify d.vect.thematic instead
of a script on top of d.vect.thematic (current solution). Since they are
converting it onto C code I will better wait.
If they are interested to look into my solutions please let me know so I
will send you my scripts. 

> On Fri, November 10, 2006 17:18, Zbigniew Perski wrote:
> > Hi,
> >
> > I am facing now with following problem:
> >
> > I have a large databases of points (more 30 000). I would like to
> > visualize them in colors according to different attributes using
> > d.vect.thematc and also store rgb information in the GRASSRGB column. I
> > noticed that both methods are incredibly slow. It is very frustrating
> > since you have to zoom and wait ages for refreshing the monitor.
> 
> There are several performance issues with d.vect.thematic:
> 
> 1) It is script-based and so if you have lots of points, it might take
> longer to calculate classes and colours than a C-based version might
> (although I don't know how much difference this would make).
> 
> 2) Gis.m seems to consider it as a new command everytime you renew the
> display in any way leading to all the calculations and rendering having to
> be redone. If you have a lot of points, this takes time.

yes. It is not very efficient way.

> 
> 3) I'm not sure the way the database connections are handled in d.vect are
> always the most efficient.
> 
> 4) d.vect in itself is not the most efficient for plotting.
yes. I was even thinkig to convert all my points to raster layer and
then create kind of pyramid to be able to see my point in different
zooming level
> 
> > My
> > database is stored using db engine. I would like to ask you if storing
> > the point database using different engine like postgresql or mysql will
> > have any impact on the performance in displaying the GRASSRGB column?
> 
> As others have said, indexing will probably help you somehwat.
> 
> > Is there any other methods to speed-up the display performance in my
> > case? I would like to add that I checked point displaying on various
> > hardware combinations and I did not noticed any significant difference.
> > It is always very slow.
> 
> I think the first important element would be to find a way to not rerun
> d.vect.thematic at every zoom or refresh...
It is crucial. 

best regards

Zbigniew